1. Field of the Invention
The present invention relates to fluid pressure operated actuators and particularly to a linear fluid cylinder actuator having self-locking means.
2. Description of the Prior Art
Heretofore in the design of fluid systems, numerous mechanisms have been employed to prevent the movement of a piston within a fluid cylinder in the event of a failure in the fluid system. One such system employs complicated valving mechanisms and circuitry which are adapted to prevent the exhausting of fluid from that side of the piston which is opposing the external load. Although such systems have functioned in an acceptable manner, resistance to the movement of the piston, and thus to the external load, in such systems diminishes with increasing use as the valves employed in the systems tend to develop volumetric losses that may go undetected, and which eventually will result in movement of the piston. In other situations when the system failure is due to a faulty piston seal, that is, fluid leakage occurring directly between the opposite sides of the piston within the fluid cylinder, most valve systems are completely useless, and the piston will be moved by the load. In many applications this movement may not only result in damage to the fluid cylinder and the equipment being operated on, but may cause injury to the operator of the fluid cylinder, as for example when such fluid cylinders are employed for use on a hoist.
Other mechanisms have been employed in combination with fluid cylinders in order to control the movement of the piston within the fluid cylinder. One such mechanism comprises a fluid cylinder having a reciprocably mounted piston with an actuating rod extending from one end, while the other end of the piston has a threaded bore adapted to receive a threaded rotating member. The other end of the rotating member extends externally of the fluid cylinder and is adapted to be engaged by a suitable locking device to prevent relative rotation between the member and the piston. When the threaded member is restrained against rotation, the piston, which likewise is restrained from rotation, is incapable of movement in an axial direction. Such prior art systems have the same disadvantages as the aforementioned fluid systems in that they are dependent upon an external locking means and an external source of power to initiate and maintain restrainment in the movement of the piston when an external load is applied to the piston.